MIT/WHOI graduate student Naomi Levine is investigating dimethylsulfide, or DMS, a naturally produced gas that influences Earth’s climate. She is studying how marine bacteria break down a larger compound (dimethylsulfoniopropionate, or DMSP) into DMS. Above, she extracts RNA from seawater samples to look for genes that code for the bacterial enzymes that degrade DMSP.
(Photo by Aimee Neeley, Bermuda Institute of Ocean Sciences)

Aboard a ship in the Sargasso Sea, Levine measures how much DMS is produced in a sample, which allows her to determine how much bacterial
DMS-producing enzymes are in the sample.
(Photo by Aimee Neeley, Bermuda Institute of Ocean Sciences)

Levine collects seawater from a sampling device, which she will analyze to look for bacterial enzymes that degrade DMSP into DMS in the ocean.
(Photo by Aimee Neeley, Bermuda Institute of Ocean Sciences)

Are these some of those penguins that Naomi Levine didn't get to see on her long research cruise to the Southern Ocean off Antarctica?
(Photo by Michael Trapp)

For Graduate Student, Research Is a Gas

Well, two gases actually, and both have key impacts on climate

When you spend 40 days on a ship in the South Atlantic, enduring equipment failures, icebergs, and the occasional surly shipmate, you should at least get to see a few penguins for your trouble.

But when Naomi Levine went to sea in the winter of 2005—her second cruise as a graduate student in the Massachusetts Institute of Technology/Woods Hole Oceanographic Institution (MIT/WHOI) Joint Program—she missed her chance.

As researchers aboard the Ronald H. Brown collected samples early each morning in the chill air, penguins would gather alongside the ship in the dawn rays, said Scott Doney, a WHOI marine chemist and Levine’s Ph.D. co-advisor.

It would have been a thrilling sight—if Levine ever got to see it. But she had to work each morning in the computer room, only coming on deck once the penguins had scattered.

“She thought we were pulling her leg about the penguins,” Doney recalled. “She never actually got to see them in the open ocean on that cruise.”

Levine, though, took the whole experience—seven-week cruise, cold weather, 12- to 14-hour workdays, no penguin sightings—with her usual good humor. “She almost always has a smile on her face,” Doney said.

“Conducting research at sea is mentally, physically, and emotionally taxing,” she said. “I would have loved to see the penguins, but that was the least of my worries.”

Legislation versus the lab

Growing up outside Boston, Levine said she was drawn to earth science by a great teacher in high school. “He showed us how you could use clues from the Earth to figure out what happened millions of years ago.”

So at Princeton University, Levine took geology courses and studied deep-Earth geochemistry. But she was also interested in environmental policy and climate, which led her to the oceans.

“I wanted to work on something more immediately relevant to society,” Levine said. “There’s so much we don’t know about the oceans and their effect on climate that it seemed like a perfect fit.”

After graduation, Levine got a job at the nonprofit organization Environmental Defense, exploring her interest in environmental policy. She worked on reports showing how climate change could affect different parts of the country. Those reports were used to encourage clean car legislation and to build congressional support for reducing carbon dioxide emissions.

She enjoyed the work, but “I wasn’t doing scientific research,” she said. “I was only reading other people’s research, and I missed being in the lab.”

The experience convinced her, however, that she wanted to focus on climate, which led her to WHOI and Doney’s lab in 2004.

Researchers have been sampling the oceans since the 1980s, on cruises like the one Levine was on in 2005, to measure the buildup of human-produced carbon in the oceans. Using computer models, Levine is evaluating the accuracy of those calculations and identifying regions of the oceans where current methods may not be very accurate.

“Ultimately, our goal is to get a better picture of how much manmade carbon dioxide is ending up in the ocean, which lets us better predict changes in Earth’s climate,” she said. (See How Long Can the Ocean Slow Global Warming?)

From CO2 to DMS

With her other Ph.D. co-advisor, WHOI marine chemist Dierdre Toole, Levine is now studying dimethylsulfide, or DMS, a naturally produced gas that influences Earth’s climate. It encourages the formation of clouds that reflect solar radiation back into space and, as a result, cool the Earth’s surface. DMS is made from a larger chemical compound called dimethylsulfoniopropionate, or DMSP, which is made by tiny marine plants, or phytoplankton. Levine’s research focuses on how DMSP is broken down by bacteria and other phytoplankton to form the DMS that eventually gets into the atmosphere. (See DMS: The Climate Gas You've Never Heard Of.)

In 2007, Levine went on seven 5-to-10-day research cruises from Bermuda to the Sargasso Sea, where she measured DMS concentrations and the rates of DMS formation. She will do 10 more cruises in 2008. She developed a method to measure the activity of bacterial enzymes that break down DMSP into DMS. That gives scientists the ability for the first time to figure out who’s responsible for the critical DMSP-to-DMS conversion—phytoplankton or bacteria.

“In large regions of the ocean, like the Sargasso where I am doing my field research, we believe that bacteria are the primary DMS producers,” Levine said. “However, there are other regions of the ocean, like the Southern Ocean around Antarctica, where phytoplankton appear to be the primary DMS producers.”

It gets more complex. The bacteria that she’s studying don’t break DMSP apart the same way every time. Scientists call it the “bacterial switch,” which sends DMSP down one of two biochemical pathways. Sometimes bacteria split DMSP to produce DMS and a carbon compound—“a good carbon food source for them, which they need to grow,” Levine said. But at other times, the bacteria break down DMSP to get at the sulfur to make amino acids and proteins, a process that doesn’t generate DMS. Some bacteria do one or the other, and some do both.

“The bacteria have to make two different enzymes to go either for the sulfur or for the carbon,” Levine said. By tracking these enzymes—and the bacterial RNA and DNA that make the enzymes—Levine can track the “bacterial switch” and investigate what factors influence the bacteria to make DMS versus processing the sulfur.

“It might be as simple as when there’s a lot of other sources of carbon around, they go after the sulfur in DMSP instead,” she said.

“Understanding when and why bacteria make DMS will allow us to better predict DMS production, and better estimate how DMS will affect the global climate in the future,” Levine said. “Global warming most likely will have significant impacts on the surface ocean and the phytoplankton and bacteria that live there. If, under new climate conditions, more DMS is produced, it will act to cool the Earth, thereby counteracting global warming. We do not know exactly how much this effect might be, but some estimates are that it could be significant. However, a decrease in DMS production will act to augment global warming.”

Levine is Toole’s first graduate student, and she says that working with Levine may be spoiling her. “I could not imagine a better student,” Toole said. “You tell her to try A, B, C and D, and she’ll come back at eight the next morning and say, ‘Done.’ ”

Sometimes that means missing the penguins.

Levine’s research is supported by the National Science Foundation; a National Defense Science and Engineering Graduate Fellowship; the MIT Scurlock Fund; and the J. Seward Johnson Fund, the Seth Sprague Educational and Charitable Foundation Fund, and the Ocean Ventures Fund—all at WHOI.

Originally published: July 24, 2008

WHOI is the world's leading non-profit oceanographic research organization. Our mission is to explore and understand the ocean and to educate scientists, students, decision-makers, and the public.